This invention relates to radiation-emitting semiconductors.
Conventional semiconductor devices often have confinement layers of InAlGaP, between which an active layer is arranged. These confinement layers constitute barriers for charge carriers. The confinement layers serve to confine the charge carriers or at least increase their retention period within the active layer.
It is desirable that the charge carriers are as completely confined as possible or that their retention period within the active layer lasts as long as possible. Outside the active layer, charge carriers do not contribute significantly to the production of radiation.
Customarily, confinement layers and active layers are lattice matched, i.e., the adjacent layers have essentially the same lattice constant. An insufficient lattice match bears the possible risk of creating strain between the confinement layer and the active layer, as well as defects in the crystal lattice. Such defects can diminish the radiation effect, since they can favor the non-radiating recombination of charge carriers.
In lattice matched confinement layers of InAlGaP, the maximally achievable barrier height, i.e., the potential energy difference through which a charge carrier would need to travel to escape the active layer, e.g., the difference between the energy levels of the active and confinement layers is relatively low. Typically, the maximum barrier height, is attained with AlInP confinement layers. Because of the limited barrier height leakage currents of charge carriers can occur. Leaked currents of charge carriers do not contribute to the creation of radiation.
A closely related problem of the charge carrier confinement exists in radiation-emitting quantum well structures of InAlGaP. Confinement of the charge carrier here takes place in the quantum well or wells. A quantum well structure of InAlGaP contains multiple subsequent quantum well and barrier layers. As with the confinement layers, a potential problem is the limited height of the barriers in the case of lattice matched layers.